Optical access is an essential part of the next-generation network, and is the main direction of the development of the optical communication technology in the next ten years. In view of the increasing requirements of various services for compatible access, research on new access means and new access techniques is of great importance.
Passive optical network (PON) is one of the important techniques for optical access. The current techniques mainly comprise wavelength division multiplexing passive optical network (WDM-PON) and time division multiplexing passive optical network (TDM-PON), wherein gigabit passive optical network (G-PON) and Ethernet network passive optical network (E-PON) are included.
The access capacity of E-PON and G-PON in a single fiber is limited, and currently there is only 32-line or 64-line. If the computer rooms of the office end are disposed across different regions, dozens of fibers have to be laid between an optical line terminal (OLT) and an optical network unit (ONU) with a distance of 10-40 km therebetween, which will not only cause a high cost for establishment and maintenance, but also will have the problem of limited fiber sources of access lines.
If the ONU of a WDM-PON adopts a laser with a specific transmission wavelength, then problems of mounting, maintenance and storage will arise. Therefore, all the ONU optical transceiving modules have to be uniform, i.e., achieving a so-called colorless ONU.
The existing solution for realizing colorless ONU either adopts a non-modulated light source provided externally to the ONU, as described in Chinese invention patent CN200510131990, or controls the tunable laser in the ONU by the OLT, as described in US invention patent US2007092256. However, externally providing a non-modulated light source to the ONU will cause a series of technical problems. For example, the optical power of the non-modulated light source will be greatly attenuated after downlink transmission. The structure of the network will be complicated in order to compensate attenuation of the optical power. Furthermore, this technique is not compatible with the technology of the current G-PON optical transceiving module.